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Age-related changes in prolactin (PRL) in systemic blood plasma, and in secretions of hypothalamic vasoactive intestinal polypeptide (VIP), an important candidate for PRL-releasing factor, and dopamine, a PRL-inhibiting factor, into the pituitary stalk blood were investigated. The experiments were performed on male urethane-chloralose-anesthetized Wistar rats of three different ages, i.e., (1) adult rats 5-8 months old, (2) middle-aged rats 12-15 months old, and (3) aged rats 24-26 months old. The concentration of immunoreactive PRL (iPRL) in systemic blood plasma of the aged rats was significantly higher than that of the adult rats (p less than 0.01). The secretion rate of hypothalamic immunoreactive VIP (iVIP) into the pituitary stalk blood was unchanged during aging, while that of dopamine was markedly increased in the aged rats in comparison with the value in both adult and middle-aged rats (p less than 0.01). These results indicate that the basal secretion of hypothalamic VIP is well maintained, while that of hypothalamic dopamine is augmented in aged rats with hyperprolactinemia. It can be assumed that the increase in the pituitary PRL secretion is a primary event during aging in rats, and that a high circulating level of PRL may facilitate the hypothalamic dopamine secretion through the activation of a negative feedback system of the hormone.

japanese journal of physiology

Age-Related Changes in Rates of Basal Secretion of Immunoreactive Vasoactive Intestinal Polypeptide and Dopamine into Pituitary Stalk Blood from the Hypothalamus in Anesthetized Male Rats.